at light
travels in a straight line, and following the path of the beam which
comes to our eyes, we are sure to locate the light.

103. Good and Bad Mirrors. As we walk along the street, we
frequently see ourselves reflected in the shop windows, in polished
metal signboards, in the metal trimmings of wagons and automobiles;
but in mirrors we get the best image of ourselves. We resent the image
given by a piece of tin, because the reflection is distorted and does
not picture us as we really are; a rough surface does not give a fair
representation; if we want a true image of ourselves, we must use a
smooth surface like a mirror as a reflector. If the water in a pond
is absolutely still, we get a clear, true image of the trees, but if
there are ripples on the surface, the reflection is blurred and
distorted. A metal roof reflects so much light that the eyes are
dazzled by it, and a whitewashed fence injures the eyes because of the
glare which comes from the reflected light. Neither of these could be
called mirrors, however, because although they reflect light, they
reflect it so irregularly that not even a suggestion of an image can
be obtained.

Most of us are sufficiently familiar with mirrors to know that the
image is a duplicate of ourselves with regard to size, shape, color,
and expression, but that it appears to be back of the mirror, while we
are actually in front of the mirror. The image appears not only behind
the mirror, but it is also exactly as far back of the mirror as we are
in front of it; if we approach the mirror, the image also draws
nearer; if we withdraw, it likewise recedes.

104. The Path of Light. If a mirror or any other polished surface is
held in the path of a sunbeam, some of the light is reflected, and by
rotating the mirror the reflected sunbeam may be made to take any
path. School children amuse themselves by reflecting sunbeams from a
mirror into their companions' faces. If the companion moves his head
in order to avoid the reflected beam, his tormentor moves or inclines
the mirror and flashes the beam back to his victim's face.

If a mirror is held so that a ray of light strikes it in a
perpendicular direction, the light is reflected backward along the
path by which it came. If, however, the light makes an angle with the
mirror, its direction is changed, and it leaves the mirror along a new
path. By observation we learn that when a beam strikes the mirror and
makes an angle of 30 deg. w